Many survivors of Saturday's plane crash in San Francisco have a surprising pattern of spine injuries that a doctor says shows how violently they were shaken despite wearing seat belts.

So far, two people are unable to move their legs — doctors don't yet know if the damage is permanent — and several others have needed surgery to stabilize their spines so they can move, said Geoffrey Manley, neurosurgery chief at San Francisco General Hospital who is overseeing their care.

Among the worst injuries are crushed vertebrae that compress the spinal cord, and ligaments so stretched and torn that they can't hold neck and back joints in place, Manley said in an interview Monday.

That 305 of the 307 passengers and crew of the Asiana jet survived the crash is remarkable, and a testimony to improvements in airline safety in recent years. More than 180 people went to hospitals with injuries, but only a small number were critically injured.

Still, Manley said even among those who suffered mild spine trauma, he is struck by a pattern that shows how their upper bodies were flung forward and then backward over the lap belts that kept them in their seats and undoubtedly saved their lives.

The injuries are somewhat reminiscent of the days before shoulder belts in cars, although much more severe, said David Okonkwo of the University of Pittsburgh Medical Center, who isn't involved with the survivors' care.

Does that mean shoulder belts in airplanes would prevent such injuries? Okonkwo said that's simplistic considering how much more speed and force are involved in a plane crash. Shoulder belts might just transfer that force to the neck, he cautioned.

"If you put in the shoulder belt, it might just move the injuries up further. Your head weighs a tremendous amount," agreed San Francisco's Manley. He hopes to study the issue, comparing survivors' injuries to where they sat.

The airline industry says adding three-point seat belts to airplanes would require major changes to seat design that would mean higher airfares and less comfort.

Some business class seats have added a type of shoulder restraint, but those seats are more like beds and often don't face forward.

Meanwhile, Okonkwo said assuming the "crash position" — leaning forward with the head as far down as possible and arms over it — can limit the spine jolting back and forth and offer some protection. It's not clear if any survivors of Saturday's crash had time to do so.

AP writer Scott Mayerowitz contributed to this report.

Asiana Flight 214 is dismantled and readied for transport to a hangar at San Francisco International Airport early on July 12. Jane Tyska, AP

Kim Yoon Ju, a crewmember of Asiana Flight 214 that crashed in San Francisco, cries after being greeted by Park Sam Koo, chairman of the Kumho-Asiana group, at the Incheon Airport in Incheon, South Korea, on July 11. Pool photo by Kim Hong-Ji

Flight attendants, who worked the ill-fated Asiana Airlines Flight 214, react after being greeted by Park Sam Koo, chairman of the Kumho-Asiana group, at the Incheon Airport in South Korea on July 11. Pool photo by Kim Hong-ji

A group of people stand in front of the wreckage of Asiana Flight 214 at San Francisco International Airport, as one of three buses reported to be carrying passengers and family members is parked next to the wreckage. Jeff Chiu, AP

Ben Levy sits with his wife, Sumi Lee Levy, on July 9 to speak about his experience as a passenger aboard Asiana Flight 214. He is wearing a yellow ribbon put on by a firefighter on the tarmac for triage after the crash. Jeff Chiu, AP

Reporters and photographers swarm CEO Yoon Young-Doo of Asiana Airlines as he makes a brief comment upon his arrival at San Francisco International Airport on July 9. Paul Chinn, San Francisco Chronicle via AP

An injured South Korean passenger, who was aboard Asiana Airlines Flight 214 when it crashed at San Francisco International Airport, is transported upon his arrival at the Incheon Airport in Incheon, South Korea, on July 10. Ahn Young-joon AP

National Transportation Safety Board Investigator in Charge Bill English and Chairman Deborah Hersman discuss the progress of the investigation into the crash of Asiana Airlines Flight 214. National Transportation Safety Board via AP

An Asiana Airlines Beoing 777 aircraft takes off from Incheon international airport in Seoul on July 9. Investigators began interviewing the cockpit crew of the Boeing 777 that crashed in San Francisco. Ed Jones, AFP/Getty Images

The July 6 crash killed three passengers, including Chinese classmates Ye Meng Yuan, left, and Wang Linjia, right. Yuan died from injuries when she was hit by an emergency vehicle following the crash. AP

In this photo by the National Transportation Safety Board, oxygen masks are seen hanging from the ceiling in the cabin interior of Asiana Airlines Flight 214 following this weekend's crash. Handout Getty Images

Survivor Fei Xiong of China speaks to the news media in San Francisco. While landing, Xiong and her 8-year-old son looked at each other, sensing something was wrong. "My son told me, 'The plane will fall down; it's too close to the sea.' I told him, 'No, baby, it's OK, weíll be fine.' And then the plane just fell down," Xiong said July 7. Jason Dearen, AP

A passenger from the Asiana Airlines crash in San Francisco arrivies at Incheon Airport, west of Seoul. The Asiana Airlines jet that crashed at San Francisco International Airport was travelling much slower than recommended, US investigators said on July 8, as the carrier confirmed that the pilot was being trained to fly the type of aircraft involved. Pool photo by Kim Hong-Ji

An unidentified family member of one of two Chinese students killed in an Asiana Airlines plane crash is escorted by airport security officers at the Pudong International Airport in Shanghai. Eugene Hoshiko, AP

An NTSB investigative team arrives to inspect the wreckage of Asiana Flight 214 during their site assessment in San Francisco. National Transportation Safety Board Chairwoman Deborah Hersman said much of the destruction isn't visible in the pictures and footage shown in the news. NTSB via Getty Images

An unidentified family member of one of two Chinese students killed in a crash of an Asiana Airlines' plane on Saturday, cries at the airline's counter as she and other family members check in for a flight to San Francisco, at Pudong International Airport in Shanghai. Eugene Hoshiko, AP

Parents of Wang Linjia are comforted by parents of some other students who were on board Asiana Airlines Flight 214 that crashed at San Francisco International Airport. Chinese media have identified the two people who died in the crash as Ye Mengyuan and Wang Linjia, both 16. AP

Geum Jae Kook, a relative of an injured passenger on Asiana Airlines Flight 214 that crashed on Saturday, checks in at the Asiana Airlines ticketing counter prior to boarding his flight to leave for San Francisco at the Incheon International Airport in South Korea. Ahn Young-joon, AP

San Francisco fire chief Joanne Hayes-White, speaks at a news conference in the museum of San Franciso International Airport where she updated the status of people that are accounted for following the crash of an Asiana flight 214. At left is San Francisco Mayor Edwin M. Lee. Behind her is Korean Consulate of San Francisco Dongman Han. Bob Stanton, USA TODAY Sports

A Boeing 777 airplane lies burned on the runway after it crash landed at San Francisco International Airport July 6 in San Francisco. The Asiana Airlines passenger aircraft coming from Seoul, South Korea. Ezra Shaw, Getty Images

People watch a news program at Seoul Railway Station in Seoul, South Korea on July 7, reporting about Asiana Airlines flight 214 which took off from Seoul and crashed while landing at San Francisco International Airport on July 6. Ahn Young-joon, AP

A couple embraces as they watch a news conference with airport and city officials at San Francisco International Airport. A Boeing 777 passenger plane en route from Seoul, South Korea crashed landed on the runway. Justin Sullivan, Getty Images

A Boeing 777 lies burned on the runway after it crash-landed Saturday at San Francisco International Airport. The Asiana Airlines passenger aircraft was en route from Seoul to San Francisco. Ezra Shaw, Getty Images

San Francisco Fire Chief Joanne Hayes-White, left, and Korean Consulate of San Francisco Dongman Han listen to speakers at a news conference after Asiana Flight 214 crashed at San Francisco International Airport in San Francisco. Jeff Chiu, AP

Sydell Straub, left, and her husband Kenneth, of Salt Lake City, wait Saturday at the Sacramento International Airport. Their flight to San Francisco was diverted to Sacramento after an Asiana Airlines jet crash-landed at San Francisco International Airport. Randall Benton, The Sacramento Bee via AP

Passengers of China Airlines who were diverted from San Francisco wait for buses to take them to hotels outside Bradley International Terminal at Los Angeles International Airport on July 6 in Los Angeles. Flights were diverted due to the crash of Asiana Flight 214 at San Francisco International Airport. Jay L. Clendenin, Los Angeles Times via AP

Passengers of China Airlines who were diverted from San Francisco wait for buses to take them to hotels outside Bradley International Terminal at Los Angeles International Airport on July 6 in Los Angeles. Flights were diverted due to the crash of Asiana Flight 214 at San Francisco International Airport. Jay L. Clendenin, Los Angeles Times via AP

Bob Merberg, foreground, sits with son Oren, 19, and daughter Maya, 16, after their flight to Rochester, N.Y., was canceled in the wake of the Asiana Airlines crash-landing at San Francisco Airport. Jeff Chiu, AP

Travelers sit in line as they wait for news on their British Airways flight after Asiana Flight 214 crashed at San Francisco International Airport. All flights in and out of the airport were stopped immediately after the crash. Jeff Chiu, AP

A firetruck stands in front of the closed international terminal at San Francisco International Airport on Saturday. A Boeing 777 Asiana Airlines passenger aircraft coming from Seoul crashed while landing. Sarah Rice, Getty Images

National Transportation Safety Board Chairwoman Deborah Hersman speaks Saturday at a news conference at Reagan National Airport in Arlington, Va. An NTSB "go-team" was departing for San Francisco where an Asiana Airlines crash-landed. Alex Wong, Getty Images

Police guard the Reflection Room at the international terminal of San Francisco International Airport on July 6. Passengers from an the Asiana Airlines flight that crash on the runway were reportedly gathered in the room. Sarah Rice, Getty Images

Officials prepare a news conference in the museum at San Francisco International Airport to update the status of people on the Asiana Airlines 214 that crashed landed earlier on July 6. Bob Stanton, USA TODAY Sports

Hermann Heider, from left, sits next to Alphonse Roig, wife Christine Roig, and their daughters Marine, 15, and Lara, 12, as they wait for news on their British Airways flight after Asiana Flight 214 crashed at San Francisco International Airport. Jeff Chiu, AP

This photo provided by Krista Seiden shows smoke rising from what a Federal Aviation Administration official says was an Asiana Airlines flight crashing while landing at San Francisco airporton July 6, 2013. Krista Seiden, AP